Method and system for reducing battery consumption in wireless transmit/receive units (WTRUs) employed in a wireless local area network/wireless wide area network (WLAN/WWAN)

ABSTRACT

Method and system for reducing battery consumption during an active session wherein an access point (AP) transmits a wireless transmit/receive unit (WTRU) a packet information regarding packets in a queue waiting for transmission to the WTRU and when the packets are to be decoded, whereby enabling the WTRU to enter or remain in an OFF mode in accordance with the packet information. The AP does not send the packets to the WTRU until the AP informs the WTRU about the packet.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application60/543,462 filed Feb. 10, 2004, and U.S. Provisional Application60/646,793 filed Jan. 25, 2005, both of which are incorporated byreference as if fully set forth.

FIELD OF INVENTION

The present invention relates to WWANs/WLANs and more particularly to amethod and apparatus for reducing the battery consumption of WTRUs in aWLAN/WWAN network.

BACKGROUND

WLAN networks currently in use typically provide for an access point(AP) to send information about queued packets for WTRUs when WTRUs arein sleep state. WTRUs enter into a sleep state by sending a message tothe AP and receiving a confirmation from the AP. This is performed at amuch lower frequency for WTRUs that are not in an active session for alonger period of time.

However, there are no techniques or apparatus presently in use in WTRUsto reduce battery consumption during an active session for everyapplication independent of the nature of application.

SUMMARY

The present invention is characterized by a “power save” feature forWTRUs. This “power save” feature can be used by all or some WTRUs in thesystem. A WTRU can inform an AP about its “power save” feature eitherduring association or any time after the association. The AP sendspackets to “power save” enabled WTRUs after indicating this informationto the WTRU. This method is employed by the WTRU for reducing batteryconsumption during an active session. The AP transmits the WTRUinformation regarding packets in a queue for that WTRU, (optionally whenthe packets are to be decoded), thereby enabling the WTRUs to enter orremain in the OFF mode until the next transmission of the packetinformation, (if there are no packets for the WTRU), or the intendedarrival time. The OFF mode is defined as the mode in which a WTRUlistens to a beacon and remains in AWAKE mode between two beacons ifthere are queued packets for the WTRU, but goes into sleep state ifthere are no queued packets indicated in the beacon for the WTRU untilthe next Beacon. The WTRU enters OFF mode from AWAKE mode by defaultafter every beacon if the beacon indicates no queued packet for theWTRU.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood from a consideration of theaccompanying drawings, wherein like elements are designated by likenumerals and, wherein:

FIG. 1 is a flow diagram of process of communication between an AP and aWTRU operating in a WLAN network and embodying the principles of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention.

FIG. 1 shows a method 10 implemented by WLAN network comprising an AP 12such as a multiport wireless AP and a WTRU 14 capable of communicatingwith the AP 12.

Hereafter, the terminology “WTRU” includes but is not limited to a userequipment, mobile station, fixed or mobile subscriber unit, pager, orany other type of device capable of operating in a wireless environmentwhich may, for example, be a personal computer (PC) or a laptop providedwith a WLAN (or WWAN) card to enable wireless transmission between thePC or laptop and the AP 12 or any other similarly equipped device. Whenreferred to hereafter, the terminology “AP” includes but is not limitedto a base station, Node-B, site controller, access point or any othertype of interfacing device in a wireless environment. Although only oneWTRU 14 is shown in FIG. 1, it should be understood that a greaternumber of WTRUs may communicate with the AP 12 utilizing the method andapparatus described herein with equal success, a single WTRU being shownmerely for purposes of simplicity. Also, the example given shows a WLAN.It should be understood that the present invention may be employed withequal success in a WWAN.

The WTRU 14 is configured to have an AWAKE state, a DOZE mode and an OFFmode in accordance with the present invention. The AWAKE and DOZE stateare part of the current WLAN standard. The present invention introducesa new state called OFF mode.

In the AWAKE state, the WTRU 14 is fully powered for normal operationwith the AP 12 and is able to receive and transmit packets at anytime.

In the OFF mode, the WTRU 14 listens to certain packet, preferablybeacon, and enters the AWAKE mode between two beacons if there arequeued packets for the WTRU 14. However, the WTRU 14 automaticallyenters into OFF mode until the next beacon if there are no queuedpackets indicated in the beacon for that WTRU 14. Unlike the DOZE mode,the WTRU 14 enters the OFF mode from the AWAKE mode by default afterevery beacon if the beacon indicates no queued packet for that WTRU 14.

Referring to FIG. 1, a method 10 for reducing battery consumption inaccordance with the present invention is explained. An AP 12, at stepS1, (step S1A is omitted from this description and is described below),creates a queue of packets to be transmitted for “power save” WTRUs. TheAP 12 withholds transmission of any packets to a WTRU 14 if the previousbeacon indicated zero queued packets for the WTRU 14. The AP 12 onlysends packets to the WTRU 14 after informing the WTRU 14 about thequeued packet in the beacon. The present invention will be mainlyexplained with reference to a beacon just for simplicity. However, itshould be noted that any packet, signal or plurality of packets, may beutilized instead of a beacon which will be explained hereinafter.

In order to enable the WTRU 14 to save battery energy, the AP 12, atstep S2, transmits information about the packets in the queue to theWTRU 14, preferably but not necessarily, in a beacon packet. Theinformation identifies the location, the number of packets and thedestination of packets in the queue. Signaling other than a beacon canbe used to send the information about packets in the queue. The signalsfrom the AP 12 sending queue information may be special packets designedfor signaling the queue information. The queue signaling may be a partof another packet or packet header. Any such packet may be periodic sothat the WTRU 14 can get into the AWAKE state to receive this packet.Alternatively, the packet may be transmitted non-periodically, whereby aprevious packet that contained the queued packet information at the APfor the WTRU 14 informs the WTRU 14 about the next time the packetinformation will be sent from the AP12.

The AP 12 may communicate information other than the identity of packetsin the queue. For example, the AP 12 may send information identifyingthose WTRUs that should remain in the active state when the AP 12 knowsit will be sending packets to such WTRUs within the superframe whichoccurs between two (2) successive beacons. The information communicatedto such WTRUs may further include those WTRUs for whom packets arequeued at the AP 12, those WTRUs to which the AP 12 is planning to sendpackets during a superframe occurring at a time between two (2) beacons,queued traffic information including traffic type, time, (i.e.,“place”), in the queue and the number of queued packets, when the packetwill be sent to the WTRU, medium access (MAC) delay, AP load, or thelike.

After the WTRU 14 is powered on, the WTRU 14 establishes an initialassociation with the AP 12 (step S3A). During this process forestablishing initial association, the WTRU 14 may inform the AP 12 thatthe WTRU 14 will implement a “power save” mechanism so that the WTRU 14may enter a OFF mode in accordance with the packet informationtransmitted from the AP 12. In response, the AP 12 may send parametersnecessary for implementing the battery saving mechanism such as thenumber of beacons with the sleep period, which may be zero (0) as adefault or any other integer value and the packet type that will be usedfor sending queued packet information which may be the beacon bydefault. Alternatively, the WTRU 14 may decide to implement the batterysaving mechanism after the initial association is established. Forexample, the WTRU 14 may initiate the battery saving mechanism after theremaining battery life (BL) falls below a predetermined threshold. Thebattery saving mechanism may be implemented automatically as a default.

The WTRU 14, having established an association with the AP 12, monitorsthe beacon at step S4 and determines if the beacon contains any queueinformation for the WTRU 14, at step S5. If there is no packet for theWTRU 14, the method 10 returns to step S3. If the beacon contains packetinformation for the WTRU 14, the method 10 advances to step S6 to decodethe timing information of the packet reception. If there is no packettiming information for the WTRU 14, the WTRU 14 enters the active modeto receive the packet (step S7). If there is packet timing informationfor the WTRU 14, the WTRU 14 sets a timer and enters the active modewhen the timer times out to receive the packet (step S9). The WTRU maystay in the AWAKE mode to receive all the packets from the AP, or maystay in the AWAKE mode only during the time interval indicated that datais transmitted to the WTRU in the packet information.

Referring back to step S7, after the WTRU 14 enters into the activemode, the WTRU 14 determines whether there are any packets to betransmitted to the AP 12 from the WTRU 14 (step S8). In the event thatthere are any packets to be transmitted at the WTRU 14, the queue isexamined to determine if the packets are time critical (step S8). If thepackets are not time-critical, the WTRU 14 withholds sending of anypackets to the AP 12 to avoid collision until the WTRU 14 receives thepacket, (or packets), intended for the WTRU 14 from the AP 12 (stepS10). If the packets at the WTRU 14 are time-critical, the WTRU 14transmits the packet whenever possible (step S11). The WTRU 14 thendetermines whether all the packets are received from the AP 12 (stepS12). If all the packets are received, the method 10 returns to step S3and the WTRU enters into OFF mode. If all the packets are not yetreceived, the method 10 returns to step S8.

In order to save additional battery life, the WTRU 14 may examine,periodically or non-periodically, remaining BL and coordinate with theAP 12 to use “power save” feature. If the remaining BL is less than athreshold, the WTRU 14 notifies the AP 12 of its “power save” featureand requests an acknowledgement (ACK) and necessary parameters, (such asfrequency of listening to the beacon and the packet type that will beused for sending queued packet information), from the AP 12.

The AP 12 may withhold informing about the queued packet at the AP inaccordance with allowed buffer at the AP 12 for each application or WTRUand quality of service (QoS) requirements of the packets, such aslatency. This ensures buffering multiple packets for the WTRU 14 at theAP 12 and making the WTRU 14 enter AWAKE mode less frequently.

In an alternative embodiment, the AP 12, at step S1A, may sendinformation to the WTRU 14 that the WTRU 14 will be polled or sentpackets at a given time (t1) after the beacon thereby enabling the WTRU14 to enter the active state at the designated time. The frequency atwhich the WTRU 14 is required to be in the active state is dependentupon the AP queue size, latency requirement of the particularapplication and battery life (and/or battery level) of the WTRU. The AP12 may alternatively provide the WTRU 14 with an interval, (i.e.,“WINDOW”), of time, (for example, a time between t1 and t2 after thebeacon), in the event that the AP 12 is not able to ensure a fixed timeof transmission.

In a case of scheduled resource allocation, the AP 12 sends packets onlyat scheduled times and provides the WTRUs with the schedulinginformation via a beacon or alternatively employing certain specialsignaling, which may be in the form of new packets designed to transfersuch information, or the information can be sent in the packet header.

1. A method for conserving power of a wireless transmit/receive unit(WTRU), the method comprising: receiving a queue identifying packetsthat are intended for the WTRU; wherein the queue includes informationregarding a location of packets in the queue waiting for transmission tothe WTRU in a scheduled transmission; entering into an OFF mode when theinformation included in the queue indicates a delay time above apredetermined threshold, wherein the delay time is based on the locationof packets in the queue waiting for transmission; entering an AWAKE modeupon expiration of the delay time; and receiving the packets at theWTRU.
 2. The method of claim 1 further comprising: transmitting anindication that the WTRU will enter the OFF mode or AWAKE mode.
 3. Themethod of claim 2 wherein the indication is transmitted during aninitial association.
 4. The method of claim 2 wherein the indication istransmitted after an initial association.
 5. The method of claim 4wherein the indication is transmitted when a level of battery life fallsbelow a predetermined threshold.
 6. The method of claim 1 wherein thequeue is received in a beacon frame.
 7. The method of claim 1 whereinthe queue is received according to predetermined schedule.
 8. The methodof claim 7 wherein the queue is received periodically.
 9. The method ofclaim 1 wherein the queue is included in a header attached to a packetreceived by the WTRU.
 10. The method of claim 1 wherein the WTRU sets atimer based on the queue and enters an AWAKE mode when the timerexpires.
 11. The method of claim 10 wherein the WTRU stays in the AWAKEmode to receive all the packets.
 12. The method of claim 10 wherein theWTRU enters the OFF mode after receiving the packets identified forreceipt by the WTRU.
 13. The method of claim 1 wherein the WTRUwithholds sending of packets during a time period identified forreceiving packets.
 14. The method of claim 1, wherein the queue furtherincludes at least one of a number of waiting packets destined for aWTRU, a WTRU identity, a traffic type, and an exact time at which apacket is to be sent to the WTRU.
 15. A power efficient wirelesstransmit/receive unit (WTRU) comprising: a receiver configured toreceive a queue identifying packets that are intended for the WTRU;wherein the queue includes information regarding a location of packetsin the queue waiting for transmission to the WTRU in a scheduledtransmission; and a processor configured to place a component of theWTRU into an OFF mode when the information included in the queueindicates a delay time above a predetermined threshold, wherein thedelay time is based on the location of packets in the queue waiting fortransmission, and to place a component of the WTRU in an AWAKE mode uponexpiration of the delay time; wherein the receiver is further configuredto receive the packets when in an AWAKE mode.
 16. The WTRU of claim 15,further comprising: a transmitter configured to transmit an indicationthat the WTRU will enter the OFF mode or AWAKE mode.
 17. The WTRU ofclaim 16, wherein the indication is transmitted during an initialassociation.
 18. The WTRU of claim 16, wherein the indication istransmitted after an initial association.
 19. The WTRU of claim 18,wherein the indication is transmitted when a level of battery life fallsbelow a predetermined threshold.
 20. The WTRU of claim 15, wherein thequeue is received in a beacon frame.
 21. The WTRU of claim 15, whereinthe queue is received according to predetermined schedule.
 22. The WTRUof claim 21, wherein the queue is received periodically.
 23. The WTRU ofclaim 15, wherein the queue is included in a header attached to a packetreceived by the WTRU.
 24. The WTRU of claim 15, wherein the processor isfurther configured to place a component of the WTRU in an OFF mode afterreceiving the packets identified for receipt by the WTRU.
 25. The WTRUof claim 15, further comprising: a transmitter for transmitting packets,wherein the transmitter is configured to withold transmitting of packetsduring a time period identified for receiving packets.
 26. The WTRU ofclaim 15, wherein the queue further includes at least one of a number ofwaiting packets destined for a WTRU, a WTRU identity, a traffic type,and an exact time at which a packet is to be sent to the WTRU.